:root {
  --bg: #eff4ff;
  --panel: rgba(255, 255, 255, 0.94);
  --line: #d4dced;
  --header: #eef3ff;
  --text: #13233b;
  --muted: #60708b;
  --accent: #2563eb;
  --accent-soft: rgba(37, 99, 235, 0.16);
  --shadow: 0 18px 44px rgba(15, 23, 42, 0.12);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: Arial, sans-serif;
  background: linear-gradient(180deg, #f8fbff 0%, var(--bg) 100%);
  color: var(--text);
}

.app-shell {
  min-height: 100vh;
  display: flex;
  flex-direction: column;
  gap: 16px;
  padding: 20px;
}

.toolbar,
.side-panel,
.grid-shell {
  background: var(--panel);
  border: 1px solid rgba(255, 255, 255, 0.9);
  box-shadow: var(--shadow);
  border-radius: 18px;
}

.toolbar {
  display: flex;
  gap: 16px;
  justify-content: space-between;
  align-items: center;
  padding: 16px 18px;
}

.toolbar-controls {
  display: flex;
  flex: 1;
  align-items: center;
  justify-content: flex-end;
  gap: 14px;
}

.brand {
  font-weight: 700;
  font-size: 1.1rem;
}

.subtitle,
.panel-hint {
  color: var(--muted);
}

.formula-wrap {
  display: flex;
  align-items: center;
  gap: 12px;
  flex: 1;
  justify-content: flex-end;
}

.structure-actions,
.structure-panel-actions {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
}

.structure-panel-actions {
  flex-direction: column;
}

.action-button {
  border: 1px solid var(--line);
  background: #fff;
  color: var(--text);
  border-radius: 10px;
  padding: 10px 12px;
  font: inherit;
  cursor: pointer;
}

.action-button:hover {
  background: #f8fbff;
}

.action-button:focus {
  outline: 2px solid var(--accent-soft);
  border-color: var(--accent);
}

.cell-label {
  min-width: 56px;
  text-align: center;
  font-weight: 700;
  background: var(--header);
  padding: 10px 12px;
  border-radius: 12px;
}

.formula-input,
.cell-editor {
  width: 100%;
  font: inherit;
  border: 1px solid var(--line);
  border-radius: 12px;
  padding: 12px 14px;
  background: #fff;
  color: var(--text);
}

.formula-input:focus,
.cell-editor:focus {
  outline: 2px solid var(--accent-soft);
  border-color: var(--accent);
}

.workspace {
  flex: 1;
  min-height: 0;
  display: grid;
  grid-template-columns: 280px minmax(0, 1fr);
  gap: 16px;
}

.side-panel {
  padding: 18px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.panel-title {
  font-weight: 700;
}

.cell-editor {
  min-height: 180px;
  resize: vertical;
}

.grid-shell {
  overflow: hidden;
  display: flex;
  flex-direction: column;
}

.column-headers,
.grid-row {
  display: grid;
  grid-template-columns: 64px repeat(26, minmax(96px, 1fr));
}

.grid-body {
  overflow: auto;
  min-height: 0;
}

.corner-cell,
.column-header,
.row-header,
.grid-cell {
  min-height: 36px;
  padding: 8px 10px;
  border-right: 1px solid var(--line);
  border-bottom: 1px solid var(--line);
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.corner-cell,
.column-header,
.row-header {
  background: var(--header);
  color: var(--muted);
  font-weight: 600;
}

.grid-cell {
  font: inherit;
  border-top: 0;
  border-left: 0;
  background: #fff;
  color: var(--text);
  text-align: left;
  cursor: pointer;
}

.grid-cell:hover {
  background: #f8fbff;
}

.grid-cell.is-selected {
  box-shadow: inset 0 0 0 2px var(--accent);
  background: #f8fbff;
}

@media (max-width: 960px) {
  .toolbar,
  .workspace {
    grid-template-columns: 1fr;
    flex-direction: column;
  }

  .toolbar {
    align-items: stretch;
  }

  .formula-wrap {
    justify-content: stretch;
  }

  .toolbar-controls {
    align-items: stretch;
    flex-direction: column;
  }
}